Various electro-optical systems have been developed for reading optical indicia, such as barcodes. A barcode is a coded pattern of graphical indicia comprised of a series of bars and spaces of varying widths. In a barcode, the bars and spaces having differing light reflecting characteristics. Some of the barcodes have a one-dimensional structure in which bars and spaces are spaced apart in one direction to form a row of patterns. Examples of one-dimensional barcodes include Uniform Product Code (UPC), which is typically used in retail store sales. Some of the barcodes have a two-dimensional structure in which multiple rows of bar and space patterns are vertically stacked to form a single barcode. Examples of two-dimensional barcodes include Code 49 and PDF417.
Systems that use one or more solid-state imagers for reading and decoding barcodes are typically referred to as imaging-based barcode readers, imaging scanners, or imaging readers. A solid-state imager generally includes a plurality of photosensitive elements or pixels aligned in one or more arrays. Examples of solid-state imagers include charged coupled devices (CCD) or complementary metal oxide semiconductor (CMOS) imaging chips.
Hand-held barcode scanners require a user to properly aim the scanner towards the desired barcode to be read. This is usually facilitated through the use of an aiming pattern that is projected onto the barcode. When there are a number of different barcodes in the field-of-view of the scanner, it can be difficult to scan the desired barcode. This issue is usually addressed by using a “Pick List” mode where only the barcode that has the aiming pattern present on the barcode is decoded. However, for aggressive barcode scanners, it is possible that an unintentional decode can occur while the user is in the process of placing the aiming pattern on the desired barcode. This occurs when the aiming spot passes over a non-desired barcode while the user is in the process of placing the aiming pattern on the desired barcode. This is particularly the case when using a long-range imager where aiming is more difficult and the potential of having many barcodes within the field-of-view is high.
One prior art solution as shown in FIG. 3 is to have a dual trigger system, where the first trigger puts the scanner into an aim mode, and the second trigger initiates the decoding. A disadvantage of this solution is the need to have two triggers which increases cost. Another prior art solution is to use a single trigger where the user pulls the trigger and the scanner remains in an aim mode for a fixed amount of time and then automatically enters a decode mode. This method has the disadvantage of assuming that the user has finished aiming the scanner before the time-out, which may not be the case. In addition, if the user has finished aiming, they must wait an additional time for the scanner to enter the decode mode. Making the aim mode timeout longer reduces the chance of a false read, but increases the decode time. Therefore, it is desirable to have better triggering mechanism for hand-held barcode scanners.